There is a known method in photogrammetry for analyzing two-dimensional images, captured on photographic film, to produce three-dimensional coordinate measurements. At least two images of an overlapping surface portion are required. Modern photogrammetry has incorporated computers to carry out many of its functions, but the process has not yet been entirely automated. Videogrammetry has added two major improvements to the art of photogrammetry. Firstly, rather than recording images on film it records images directly on opto-electronic imaging devices, such as photosensitive diodes or other imaging surfaces. And secondly, since the images are immediately digitized and stored in a computer, they are readily accessible to manipulation and analysis by computational methods.
Attempts have been made to develop better systems and methods for measuring three-dimensional spatial coordinates. For example, U.S. Pat. No. 5,589,942 dated Dec. 31, 1996, granted to Gordon, for a "Real time three dimensional sensing system" discloses a system which utilizes two flexibly located cameras for receiving and recording visual information with respect to a sensed object illuminated by a series of light planes. Each pixel of each image is converted to a digital word and the words are grouped into stripes, each stripe comprising contiguous pixels. One pixel of each stripe in one image is selected and an epi-polar line of that point is drawn in the other image. The three dimensional coordinate of each selected point is determined by establishing the point on said epi-polar line which also lies on a stripe in the second image and which is closest to a known light plane. This system uses a complex pattern of projected stripes, which creates difficulties in finding homologous points in the pair of images, and leads to false positives and false negatives in homologous point identification. The system requires the light plane to be known.
U.S. Pat. No. 4,627,734, dated Dec. 9, 1986, granted to Rioux, for a "Three dimensional imaging device and method" discloses a three-dimensional imaging system operating in accordance with the known active triangulation method, and employing a laser beam that is projected onto an area of the surface to be examined. The solution is characterized by synchronized scanning of projected and deflected beams. The main disadvantage of the system consists in the fact that the position and orientation of the projected light beam must be known in order to calculate three dimensional coordinates.
U.S. Pat. No. 5,440,392 dated Aug. 8, 1995, granted to Pettersen et al. for a "Method and system for point by point measurement of spatial coordinates" describes a technical solution for point by point measurement of spatial coordinates. A touch probe, including three point-sized light sources at known local coordinates, touches the point to be measured. Using a camera to acquire an image of the three light sources, the system calculates the three dimensional coordinates of the point touched. It is obvious that this solution requires physically touching the object to be measured and is time-consuming.